Conventionally, there has been known a technique structured such that a diesel particulate filter (or an NOx catalyst) or the like is provided as an exhaust gas purifying device (an after treatment device) in an exhaust gas discharge route of the diesel engine, and the exhaust gas discharged out of the diesel engine is purified by the diesel particulate filter (or the NOx catalyst) or the like (refer to Patent Document 1, Patent Document 2, and Patent Document 3). Further, there has been known a technique in which a filter case (an inner case) is provided within a casing (an outer case), and a particulate filter is arranged within the filter case (see Patent Document 4).